±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,

RS-232 Transceivers with AutoShutdown

6

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Pin Description

-5.5V generated by the charge pump

V-

RS-232 Receiver Inputs

R_IN

TTL/CMOS Receiver Outputs

R_OUT

Output of the Valid Signal Detector. INVALID is enabled high if a valid

RS-232 level is present on any receiver input.

INVALID

+5.5V generated by the charge pump

V+

Negative terminal of the voltage doubler Charge-Pump Capacitor

C1-

Positive terminal of inverting Charge-Pump Capacitor

C2+

Negative terminal of inverting Charge-Pump Capacitor

C2-

Positive terminal of the voltage doubler Charge-Pump Capacitor

C1+

Receiver Enable Control. Drive low for normal operation. Drive high to

force the receiver outputs (R_OUT) into a high-impedance state.

EN

FUNCTION

TTL/CMOS Transmitter Inputs

T_IN

Drive high to override automatic circuitry keeping transmitters and

charge pump on (FORCEOFF must be high) (Table 1).

FORCEON

_______________Detailed Description

Dual Charge-Pump Voltage Converter

The MAX3221E/MAX3223E/MAX3243E’s internal power

supply consists of a regulated dual charge pump that

provides output voltages of +5.5V (doubling charge

pump) and -5.5V (inverting charge pump), over the

in discontinuous mode: if the output voltages are less

than 5.5V, the charge pumps are enabled; if the output

voltages exceed 5.5V, the charge pumps are disabled.

Each charge pump requires a flying capacitor (C1, C2)

and a reservoir capacitor (C3, C4) to generate the V+

and V- supplies.

RS-232 Transmitters

The transmitters are inverting level translators that con-

vert CMOS-logic levels to 5.0V EIA/TIA-232 levels. They

guarantee a 250kbps data rate with worst-case loads

of 3k

Ω in parallel with 1000pF, providing compatibility

with PC-to-PC communication software such as

LapLink™. Transmitters can be paralleled to drive mul-

tiple receivers. The MAX3243E has been specifically

designed to drive serial mice. Figure 1 shows a com-

plete system connection.

When FORCEOFF is driven to ground, or the

AutoShutdown circuitry senses invalid voltage levels on

all receiver inputs, the transmitters are disabled and the

outputs are forced into a high-impedance state. When

powered off or shut down, the output can be driven up

to ±12V. The transmitter inputs do not have pull-up

resistors.

7

8

9

10

3

4

5

6

2

1

11

12

NAME

MAX3221E

RS-232 Transmitter Outputs

T_OUT

13

TTL/CMOS Noninverting Complementary Receiver Output. Always

active.

R2OUTB

—

7

9, 16

10, 15

11

3

4

5

6

2

1

12, 13

14

3

4–8

15–19

21

27

24

1

2

28

—

12, 13, 14

23

MAX3223E

8, 17

MAX3243E

9, 10, 11

—

20

PIN

14

18

25

GND

Ground

15

19

26

+3.0V to +5.5V Supply Voltage

16

20

22

FORCEOFF

Force-Off Input, active low. Drive low to shut down transmitters,

receivers (MAX3243E, except R2OUTB), and on-board charge pump.

This overrides all automatic circuitry and FORCEON (Table 1).

LapLink is a trademark of Traveling Software.